Improper parsing of HTTP requests in Pallets Werkzeug v2.1.0 and below allows attackers to perform HTTP Request Smuggling using a crafted HTTP request with multiple requests included inside the body. NOTE: the vendor's position is that this behavior can only occur in unsupported configurations involving development mode and an HTTP server from outside the Werkzeug project
https://github.com/pallets/werkzeug/issues/2420
https://github.com/pallets/werkzeug/commit/9a3a981d70d2e9ec3344b5192f86fcaf3210cd85